Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: timmyjoe on July 02, 2021, 07:12:22 pm
-
Just finished a 5E3 build. My first build.
I'm getting a buzz or rattle with several low notes. Played it outside just to be sure it wasn't from the something shaking in the house. So some notes are good and some buzz. Changed cabinets to see if it was something loose. Does it with both.
Someone in another forum thought it was one of the power tubes. I've got some old tubes that I could try. Not sure if they are any good though. Any harm in swapping them for a test?
-
you can swap, bias, and see what happens.
did you use a kit or source components yourself? I built one out of a hammond donor and had problems with the low end. Wound up reducing the first coupling caps from 0.1 to 0.047. This is a common issue.
-
Check that the input Jack tip-switch contacts are closing firmly (and not just marginally closing, which can cause buzzing/rattling/ microphonic chassis symptoms). The tip switch contacts can get bent when installing the jacks, depending on how you held onto the jacks to tighten them up.
-
google & search this forum for "ghost notes".
-
I had bad joints that would rattle on just one note.
-
you can swap, bias, and see what happens.
did you use a kit or source components yourself? I built one out of a hammond donor and had problems with the low end. Wound up reducing the first coupling caps from 0.1 to 0.047. This is a common issue.
It's a 5E3 , that's cathode biased, so you can be pretty sure there's no need for rebiasing, given the tubes are the same type.
-
fair. still check it though.
-
Still haven't solved the rattle. Sometimes it is there, sometimes not. The notes it is active on changes too.
Tubeswell, what should I do to check the input jacks? Just bend the tip prongs in a bit to help them make the connection?
I've checked the tubes for microphonic by tapping on them. Nothing.
-
Is the amp in the cabinet?
The reason I ask is that I was scratching my head about a weird rattle while outside the cab… turned out to be the cage nuts free to rattle within the clips with out the bolt securing it tightly.
Probably, not this simple, but…
-
external cab. Tried two different cabinets and they both get rattle.
But, I think I can say for sure it gets worse as the amp stays on. And it is in both channels, but worse in the bright channel.
So maybe a bad joint just after the pre-amp tubes? :think1:
-
Tubeswell, what should I do to check the input jacks? Just bend the tip prongs in a bit to help them make the connection?
You can tell if you drag your fingertip (fingerprint side) lightly across the edge of the jack tip and it makes a vibrating sound. (Obviously you should be careful - if in doubt chopstick it)
-
Try playing the note that causes the buzz, and while it's buzzing, slightly push down on each tube. I found the buzzing was caused by a slightly microphonic output tube.
-
Got a looper pedal? Record the buzz inducing note into it and then you’ve got your hands free to explore and trace.
-
Yeah, finally found some of the noise with a looper pedal. Amazing how far the wood floors of house take the vibrations. Cans of polyurethane was a big part of it. Being deaf in one ear makes it hard to chase these things down.
Going to try to wedge some foam around the speaker cabinet and the cabinet I have it stored in. Think the large cabinet is spreading the vibrations. (Have to speaker cabinet inside other cabinet to keep the cats from loving it with claws.)
-
Yeah, finally found some of the noise with a looper pedal. Amazing how far the wood floors of house take the vibrations. Cans of polyurethane was a big part of it. Being deaf in one ear makes it hard to chase these things down.
Going to try to wedge some foam around the speaker cabinet and the cabinet I have it stored in. Think the large cabinet is spreading the vibrations. (Have to speaker cabinet inside other cabinet to keep the cats from loving it with claws.)
I would still suspect a loosely closing input jack tip switch contact (unless you have confirmed that each input jack tip switch contact is closing firmly with no plug inserted)
-
Been working on the amp again and got more questions.
1. Speaker Change- I've got a Jensen p12r. Looking like it is a bad pairing in that the speaker has a loose low end and the 5E3 is very thick on the bass. Speaker flubbing out? Maybe change to Weber a125?
2. I changed the filter caps from 16ufs to 20/10/10. It helped a bit with the buzz. But heck no. Lost all the gain and breakup. Guess I'll go back to the 16uf. Should I really try the .047 coupling cap fix or try the speaker first? Really like the original sound, so worried about any cap change. I bought some .022 caps to do this change, but yeah, maybe .047 would be enough.
3. When working on the amp I found that I had reversed electrolytic capacitor that goes to pin 3 on the 12Ay7. I don't have a spare, so just flipped it to the correct orientation. Would this do anything to the circuit, or just not charge it because it is oriented wrong?
4. Tubewells, was thinking you meant check the output jacks, but now see you said the input. Being that the rattle can happen on all 4 jacks, I'm guessing I'm not that unlucky..... right?
Thanks again for all who
-
Finally got it figured out... or at least the noise is gone.
1. I really padded around the cabinet to keep the vibrations from easily rattling things in the house.
2. When working on the amp some more I found that I had installed the 25uf 50v capacitor backwards next to V2. Could that of caused the low frequency flub? I replaced it with a unblown cap.
Last lesson- I tried some of the cap mods that dropped the values from .1 down to .022 or .044. No way I would do that again. Totally killed the texture of the low notes.
-
2. When working on the amp some more I found that I had installed the 25uf 50v capacitor backwards next to V2. Could that of caused the low frequency flub? I replaced it with a unblown cap.
Well, after changing that K bypass cap, did the low frequency flub stop?
-
Yes Willabe. After fixing the K bypass cap, things are fine. Flub gone.